Technical Document | TD-113

Why Annealed, Heat Strengthened And Tempered Glass All Deflect the Same Amount

Deflection As a result, even though basic material stiffness When a solid material like a steel beam has a is unchanged by heat strengthening and load applied to it, the load creates a in the tempering, heat strengthened glass is about two beam and the beam deflects. The amount of times stronger and tempered glass about four deflection depends on the size and shape of the times stronger than annealed glass under uniform beam, and the stiffness of the material of which static loads like wind loading. the beam is made, and the amount of load that is applied. This means that for the same size light, same thickness and same applied load, annealed, heat The engineering term for material stiffness is strengthened and tempered glass will each have a modulus of elasticity or Young’s modulus. different probability of breakage, even though Materials with higher modulus numbers are the deflection for each of these glass types will stiffer than materials with lower modulus be equal. numbers. Example: a light of glass 60" x 72", 6mm Young's modulus for some typical materials thickness with an applied wind load of 40 psf Carbon Steel 30,000,000 psi will have the following structural characteristics: Chromium 36,000,000 psi Aluminum 10,000 000 psi MAXIMUM *PROBABILITY Vitro 10,600,000 psi GLASS TYPE DEFLECTION OF BREAKAGE (INCHES) The above numbers indicate that carbon steel is 3 times stiffer than aluminum, and that glass is just Annealed 47 per thousand 0.78 slightly stiffer than aluminum. In actual practice, this would mean that if you have two beams of Heat 1 per hundred 0.78 equal size, one of steel and the other of Strengthened thousand aluminum, the aluminum beam will deflect 3 times further than the steel beam if loaded with Tempered 1 per million 0.78 the same load.

Tempered or Heat Strengthened Glass *Probability of breakage indicates the number of When glass is tempered or heat strengthened, its lights that may be expected to break at the initial modulus of elasticity remains unchanged. This occurrence of the design wind load. In the U.S., means that for the same size and thickness of architects generally choose the design probability glass, the deflection for the same applied load of breakage for vertical glazing in buildings at 8 will be exactly the same whether the glass is per 1000. In this case, then, Vitro would not annealed, heat strengthened or tempered. recommend annealed glass for this application.

Even though the deflection is the same, however, a very significant difference does exist. The heat strengthening and tempering processes impart a surface and edge compression envelope around the glass. At the same time, balancing center tension stresses are created in the glass, maintaining equilibrium between outer compression stress and internal tension stress in the final product.

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Glass Technical Document | TD-113

Why Annealed, Heat Strengthened And Tempered Glass All Deflect the Same Amount

HISTORY TABLE ITEM DATE DESCRIPTION Original Publication February, 1993 Revision #1 1/14/2001 Revised & Transferred to TD-113 Revision #2 2016-10-04 Updated to Vitro Logo and format

This document is intended to inform and assist the reader in the application, use, and maintenance of Vitro Flat Glass products. Actual performance and results can vary depending on the circumstances. Vitro makes no warranty or guarantee as to the results to be obtained from the use of all or any portion of the information provided herein, and hereby disclaims any liability for personal injury, property damage, product insufficiency, or any other damages of any kind or nature arising from the reader's use of the information contained herein.

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